We have succeeded in demonstrating the existence of a rapid expansion of the volume of the post-synaptic elements during synaptic transmission. This demonstration was carried out by stimulating the ray electric organ (which is rich in cholinergic terminals) enclosed in a sealed plastic chamber. The rearrangement of the water molecules bound to the electrically charged sites in the post-synaptic elements is at the base of the observed volume expansion. Quite recently, we found swelling of the amphibian cutaneous glands following excitation of their adrenergic nerve terminals. This swelling was found to be accompanied also by heat production. The causal relationship of hte heat production and swelling with the electric response of the gland is now being investigated.